1. Field of the Invention
This invention relates to a video signal processing apparatus including an interpolator controlled by a motion detector.
2. Description of the Prior Art
When a display device reproduces an image from a video signal by interlaced scanning, the reproduced image tends to be contaminated by line flickers. The interlaced scanning is a main cause of the line flickers. To remove such line flickers, it is known to interpolate scanning lines and thereby to enable progressive scanning.
A prior-art video signal processing apparatus includes an inter-line interpolator, an inter-field interpolator, and a motion detector which detects a motion of an object on the basis of a signal representative of a luminance difference between frames of a video signal. In the presence of a detection output from the motion detector, an interpolation signal generated by the inter-line interpolator is selected. In the absence of a detection output from the motion detector, an interpolation signal generated by the inter-field interpolator is selected or a weighted addition of the interpolation signals generated by the two interpolators is used.
In the above-mentioned prior-art video signal processing apparatus, a certain condition such as a slight vibration of an object in a vertical direction or a sudden disappearance of a horizontally-extending edge of a superimposed letter tend to be detected as a motion which causes a change of the interpolation from the inter-field type to the inter-line type. It is generally better to maintain the inter-field interpolation under such a certain condition from the standpoint of the quality of a reproduced image.